/*
* Copyright 2003-2005 Sun Microsystems, Inc. All Rights Reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Sun designates this
* particular file as subject to the "Classpath" exception as provided
* by Sun in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
* CA 95054 USA or visit www.sun.com if you need additional information or
* have any questions.
*/
package javax.xml.xpath;
import javax.xml.namespace.QName;
/**
* <p><code>XPathFunctionResolver</code> provides access to the set of user defined <code>XPathFunction</code>s.</p>
*
* <p>XPath functions are resolved by name and arity.
* The resolver is not needed for XPath built-in functions and the resolver
* <strong><em>cannot</em></strong> be used to override those functions.</p>
*
* <p>In particular, the resolver is only called for functions in an another
* namespace (functions with an explicit prefix). This means that you cannot
* use the <code>XPathFunctionResolver</code> to implement specifications
* like <a href="http://www.w3.org/TR/xmldsig-core/">XML-Signature Syntax
* and Processing</a> which extend the function library of XPath 1.0 in the
* same namespace. This is a consequence of the design of the resolver.</p>
*
* <p>If you wish to implement additional built-in functions, you will have to
* extend the underlying implementation directly.</p>
*
* @author <a href="mailto:Norman.Walsh@Sun.com">Norman Walsh</a>
* @author <a href="mailto:Jeff.Suttor@Sun.com">Jeff Suttor</a>
* @see <a href="http://www.w3.org/TR/xpath#corelib">XML Path Language (XPath) Version 1.0, Core Function Library</a>
* @since 1.5
*/
public interface XPathFunctionResolver {
/**
* <p>Find a function in the set of available functions.</p>
*
* <p>If <code>functionName</code> or <code>arity</code> is <code>null</code>, then a <code>NullPointerException</code> is thrown.</p>
*
* @param functionName The function name.
* @param arity The number of arguments that the returned function must accept.
*
* @return The function or <code>null</code> if no function named <code>functionName</code> with <code>arity</code> arguments exists.
*
* @throws NullPointerException If <code>functionName</code> or <code>arity</code> is <code>null</code>.
*/
public XPathFunction resolveFunction(QName functionName, int arity);
}